Al Viro 4b0fe71fb3 shmem: fix recovery on rename failures ...

[ Upstream commit e1b4c6a583 ]

maple_tree insertions can fail if we are seriously short on memory;
simple_offset_rename() does not recover well if it runs into that.
The same goes for simple_offset_rename_exchange().

Moreover, shmem_whiteout() expects that if it succeeds, the caller will
progress to d_move(), i.e. that shmem_rename2() won't fail past the
successful call of shmem_whiteout().

Not hard to fix, fortunately - mtree_store() can't fail if the index we
are trying to store into is already present in the tree as a singleton.

For simple_offset_rename_exchange() that's enough - we just need to be
careful about the order of operations.

For simple_offset_rename() solution is to preinsert the target into the
tree for new_dir; the rest can be done without any potentially failing
operations.

That preinsertion has to be done in shmem_rename2() rather than in
simple_offset_rename() itself - otherwise we'd need to deal with the
possibility of failure after successful shmem_whiteout().

Fixes: a2e459555c ("shmem: stable directory offsets")
Reviewed-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

2026-01-08 10:13:54 +01:00

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